Headphone amplifier



FIG. 1 is a front and top perspective view of a headphone amplifier, showing my new design;

FIG. 2 is a rear and bottom perspective view thereof;

FIG. 3 is a front elevation view thereof;

FIG. 4 is a rear elevation view thereof;

FIG. 5 is a left side elevation view thereof;

FIG. 6 is a right side elevation view thereof;

FIG. 7 is a top plan view thereof; and,

FIG. 8 is a bottom plan view thereof.

The broken lines in the figures illustrate portions of the headphone amplifier that form no part of the claimed design. 

CLAIM The ornamental design for a headphone amplifier, as shown and described. 